FWIW, I've been getting these often with my HTC Incredible. Clearing the data in HTC Sense seemed to be the one thing that solved the issue for me. (I'm using Zeam launcher besides.)
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garyMay 29 '11 at 15:37

I tried all the standard cache cleaning and uninstalling updates which helped a lot. I tried storage analyser but that didn't help the internal storage. Wasn't keen on rooting the phone. Then I came across Clean Master and used it on my wife's Samsung Ace which is notoriously short on internal memory and no option to move most apps to the SD card. So far so good.

Ok guys I was having this problem a couple of days ago... I reset my device, deleted all the apps, had LOADS of free space but when I tried to install something it would tell me "insufficient storage available"

I searched everywhere, for more than a week, and found nothing. Now, i found the solution, and want to help everyone that is happening the problem!

Get Storage Analyser then open it, and you will see that instead of having free space, you will have -xxxx!

Yes! A negative number! According to my phone I had -8GB of space! There was this rogue app from Gameloft that used up all my space! And didn't get deleted with a factory reset!

Open the Storage Analyser and delete the huge app/folder! Then reboot and the problem will be solved! I promise 100% that this works. I recommend opening the app once a week and deleting the useless big stuff!

It may be time for you to start removing old applications that you no longer use or don't use very frequently. You've already moved your apps to the SD card and cleared your caches, there isn't much more you can do.